| Description |
In the Gas Hills District, located near Riverton, Wyoming, a clay mineral assemblage was identified within and around the ore bodies, which includes 5 to 11 percent kaolinite, with the highest amount in the ore body, 4 to 7 percent smectite, with the highest amount being in the reduced sandstone, and 5 to 8 percent illite, with the highest amount in the oxidized sandstone. This assemblage can be classified as argillic alteration. Three different habits associated with the clays were identified that change systematically from the reduced sandstone to the oxidized sandstone. These textural differences are a result of changes in fluid composition over time. The disseminated habit in the reduced sandstone is likely formed during diagenesis. The clot-like habit in the oxidized sandstone was created at the onset of oxidation and near surface weathering. The grain replacement habit seen in the ore body is a result of alteration during mineralization. Porosity changes considerably, from an average of 5 percent in the reduced sandstone to 23 percent in the oxidized sandstone. The controls on porosity include the distribution of clays, the habit of the clay, and the presence of authigenic quartz in the ore body. K, P, Tl, As, Rb, and Zr are correlated with uranium and have increased concentrations in the ore zone. Cu, Ti, Mg, Zn, Ni, and Cr are most concentrated in the unaltered, reduced sandstone. K and Rb are the only elements that increased in concentration in the distal oxidized sandstone. In the mineralized sandstone, U correlates strongly with Zn, Co, Mg, and has a negative correlation with V. This is due to differences in solubility. In the reduced sandstone, U correlates with Mo and Tl. In the oxidized sandstone, U strongly correlates with As, Fe, and Co. Rare earth elements in the mineralized sandstone increase as compared to the reduced sandstone by a factor of five. The LREE move separately from the HREE. The LREE vary in concentration within the oxidized, reduced, and mineralized sandstones. |
